There has been many previous solar collector systems described which provide energy savings particularly for meeting heating or hot water requirements. Although such systems have been known for some time, their implementation has been inhibited by the high cost of solar collector units and the relatively lower cost of common fossil fuels. With the cost of all fuels now escalating, solar heating units have become more attractive, yet their usage is still restricted due in major part to the substantial initial expense involved in purchasing collector units.
Existing solar collectors tend to be either one of three types. Concentration type collectors localize the sun's light on a particular heat conductive member which transfers the heat to a circulating fluid which can then communicate the heat to a receptor. The labor and material expense involved in the manufacture of these focusing collectors make them impractical for many applications. In addition to the economic considerations, typical concentration collectors are further limited in that they are effective for only a narrow angle of sunlight outside of which their effectiveness decreases dramatically.
Metallic pipe collectors typically include a black, fluid carrying pipe spaced between a glass or plastic cover and an insulated base. These devices often employ coiled piping or zigzagging in convolutions in a given plane requiring numerous flow restricting elbows and considerable lengths of metallic piping. Thermal inefficiencies result from the excessive spacing of the convolutions which permits radiation of much of the solar energy back into the atmosphere. Economic inefficiencies further include the excessive labor and material costs inherent in the production of the device.
The present invention is of the third variety utilizing a flat plate collector. This type system makes use of flat surfaces to absorb the solar energy, and can receive light from a wide variety of angles. Although a considerable number of flat plate collector systems exist, none of these systems use the unitized mode of construction operable over wide temperature ranges as does the present invention. H. E. Stoutin, U.S. Pat. No. 3,918,430, teaches a light weight plastic film solar collector utilizing a plate collector in a plastic frame. Stout, however, does not disclose the use of fluid passageways integral to the plastic frame, but rather requires the installation of multiple film layers and further necessitates the use of a fabricated solar ply which makes the system more expensive. In addition, the use of a plastic foam insulation base in the patent results in undesirable temperature limitations of which the inventors were apparently unaware. E. W. Gough in U.S. Pat. No. 3,076,450, teaches a plastic solar heater. This patent uses a polyurethane foam plastic base which includes an undulated top that defines a series of parallel water channels. The application of a black plastic liner to the surface of the plastic base, as described in the reference, requires additional manufacturing and results in direct contact between the heat conducting fluid and the thin plastic liner. If such contact is continuous, the result is likely to be the deterioration of the plastic liner necessitating extensive repair procedures to the replacement of the entire unit.
Other prior art devices, including that described in U.S. Pat. No. 3,965,887 issued to Gramer, et al., discloses the use of a plastic base member in conjunction with a metallic absorber plate. In such a heat attracting system wherein materials having widely different thermal expansion rates are joined, their differing reactions to the applied cause stress to develop along their contact surfaces.
As one skilled in the art will recognize, stagnation temperatures in excess of 300.degree. F. may develop within a drained or undrained solar collector. These temperatures cause considerable stress to develop along the bond line between the heat absorbent plate and base member. Reliable operation of the device is, therefore, limited to a narrower temperature bond with a substantial likelihood of bond line failure at the higher, stagnation temperatures. Similar limitations may develop with the use of glass/plastic devices, or even plastic/plastic devices wherein the materials used have differing thermal expansion coefficients.
In the system proposed by Gramer, this problem is recognized and addressed through the use of elastic adhesive means to bond the absorber plate to the base member. This construction represents one approach to preserving bonding characteristics in the face of the grossly uneven expansion of plastic and metallic elements. The present invention by contract provides high temperature operative capacity through the use of thermally compatible plastic materials, thereby eliminating the need for elastic adhesive means.
Although the above described systems have assisted in solving problems present in the design of an efficient solar collector, neither these nor other systems proved entirely satisfactory for the reason that no truly cost effective low pressure collector system has been proposed until the emergence of the present system.
While the use of plastic components has been proposed for use in connection with one or more portions of a solar collector system, no previous constructions have been proposed which so match collector components according to their thermal characteristics to allow continuous system operation through both high and low temperature conditions.
Accordingly, it is an object of the present invention to provide a new and improved solar heating system which is operative over wide temperature ranges.
It is another object of the present invention to provide a durable non-corrosive solar heating system which is not easily damaged, can be manufactured at low cost, and can utilize copper plumbing.
It is also an object of the present invention to provide an inexpensive and self-draining solar heating system requiring minimal maintenance and suitable for high temperature operation associated with shut down.
It is a further object of the present invention to provide a reliable solar collector assembly wherein bonding between the absorber plate and the collector base is maintained over a wide range of operating temperatures.
It is another object of the present invention to provide a solar collector assembly in which the various components are composed of thermally compatible materials which react similarly to the ambient thermal conditions.
A further object of the present invention is to provide a solar collector assembly wherein even liquid flow distribution is assured regardless of how the assembly is turned.
It is a still further object of this invention to provide a solar collector system which utilizes an inexpensive molded plastic collector base which makes fluid connection, installation, interconnection of multiple units and any necessary repair relatively simple and extremely cost effective in both terms of labor and materials.
In accomplishing the foregoing objects, there has been provided, according to one embodiment of the invention, a solar collector assembly having a molded one piece collector assembly frame including an upper ribbed surface defining a plurality of capillary passages. An absorber plate is secured to the upper ribbed surface of the frame to seal the capillary passages and to transfer heat to the liquid therein. The collector frame and absorber plate are composed of identical or similar plastic materials such that both components exhibit similar thermal expansion characteristics, thereby minimizing bondline stress between the components. Thermal insulating material may be interposed beneath the assembly frame upper surface. Even fluid distribution across the collector surface is accomplished by forming standoff regions in diagonally opposite corners of the frame upper ribbed surface. Even fluid distribution across the collector upper surface is thereby assured regardless of how the assembly is turned.
These and other objects and advantages of the invention will be apparent from the following description and claims, the novelty consisting of the feature of construction, combination of parts, the unique relations of the members and the operation thereof, all as more completely outlined herein and particularly pointed out in the appended claims.